feat(waitlist): optional event waitlist with FIFO promote.

Commercial calendars opt in via settings.waitlist_enabled; join when full;
auto-promote on cancel/decline/expire with email and in-app notify.

Refs EventHub/EventHubBack#72

include/records.hrl

@@ -200,6 +200,16 @@
   updated_at      :: calendar:datetime()
 }).
 
+%% ------------------- Лист ожидания (commercial, settings.waitlist_enabled) ----
+-record(waitlist_entry, {
+  id              :: binary(),
+  event_id        :: binary(),
+  user_id         :: binary(),
+  status          :: waiting | promoted | left,
+  created_at      :: calendar:datetime(),
+  updated_at      :: calendar:datetime()
+}).
+
 %% ------------------- Отзывы ------------------------------------------
 -record(review, {
   id              :: binary(),
@@ -319,7 +329,7 @@
   id              :: binary(),
   user_id         :: binary(),
   type            :: booking_confirmed | event_reminder | event_cancelled |
-                     specialist_invite | custom,
+                     specialist_invite | waitlist_promoted | custom,
   title           :: binary(),
   body            :: binary(),
   is_read         :: boolean(),